Relationship between the ATP content measured at three imbibition times and germination of onion seeds during storage at 3, 15 and 30°C

The possibility of using ATP content as an indicator of seed quality was studied in onion seeds {Allium cepa cv. Wädenswil). The percentage germination and ATP content of imbibed seeds were compared during 145 weeks of storage at three temperatures (3, 15 and 30°C). ATP content, which was undetectable in airdried seeds (moisture content: 9%, w/w), increased rapidly as a function of imbibition time, as did the fresh weight and respiration rate, reaching a steady-state level after about 17 h. After 36 weeks of storage, the rate of ATP formation was greater for the seeds stored at 3°C than for those kept at 15 and 30°C. Furthermore, the onset of ATP synthesis was delayed. These phenomena, which are likely to be an expression of seed ageing, are useful indicators, allowing the prediction of the loss of seed viability before the decrease in percentage germination which occurred beyond 36 weeks of storage. In addition, the correlation between ATP content and germination capacity of seeds during 145 weeks of storage was excellent (r=0.95 at 15°C and 0.97 at 30°C), provided that a 17 h-imbibition time, specific for onion seeds, was chosen. These results are discussed in terms of the controversy concerning the correlation between the ATP content and germination percentage of seed

Mutation of a single residue, β-glutamate-20, alters protein–lipid interactions of light harvesting complex II

It is well established that assembly of the peripheral antenna complex, LH2, is required for proper photosynthetic membrane biogenesis in the purple bacterium Rhodobacter sphaeroides. The underlying interactions are, as yet, not understood. Here we examined the relationship between the morphology of the photosynthetic membrane and the lipid–protein interactions at the LH2–lipid interface. The non-bilayer lipid, phosphatidylethanolamine, is shown to be highly enriched in the boundary lipid phase of LH2. Sequence alignments indicate a putative lipid binding site, which includes β-glutamate-20 and the adjacent carotenoid end group. Replacement of β-glutamate-20 with alanine results in significant reduction of phosphatidylethanolamine and concomitant raise in phosphatidylcholine in the boundary lipid phase of LH2 without altering the lipid composition of the bulk phase. The morphology of the LH2 housing membrane is, however, unaffected by the amino acid replacement. In contrast, simultaneous modification of glutamate-20 and exchange of the carotenoid sphaeroidenone with neurosporene results in significant enlargement of the vesicular membrane invaginations. These findings suggest that the LH2 complex, specifically β-glutamate-20 and the carotenoids' polar head group, contribute to the shaping of the photosynthetic membrane by specific interactions with surrounding lipid molecules